Chronic Fatigue Syndrome (CFS) is a complex disease with a prevalence as high as 1%. CFS involves the nervous, hormonal and immune systems with symptoms that include fatigue, sleep disturbances, malaise, muscle aches, migraines, gastrointestinal complaints and cognitive problems. There may be some mitochondrial dysfunction in CFS patients. Many CFS patients demonstrate abnormal hypothalamic-pituitary- adrenal (HPA) axis activity, while stress worsens symptoms. Central and peripheral cytokines produced in response to viral infections or other inflammatory stimuli may be implicated, but there is no distinct pattern. CFS is often comorbid with other disorders that include fibromyalgia, interstitial cystitis (1C), irritable bowel syndrome (IBS), migraines and post-traumatic stress disorder. Neuroimmune interactions in CFS are still unknown creating a vacuum in diagnosis and treatment. Mast cells and their mediators have been implicated in all diseases that are comorbid with CFS. Brain mast cells are abundant in the median eminence where they are juxtaposed to corticotropin-releasing hormone (CRH)-positive neurons and CRH is secreted under stress and we showed that CRH activates mast cells through CRHR-1 leading to release of vascular endothelial growth factor (VEGF), increased vascular permeability and blood-brain-barrier (BBB) disruption. We recently showed an inverse relationship between expression of the mitochondrial uncoupling protein 2 (UCP2), which also regulates production of reactive oxygen species (ROS) and cytosolic calcium, and mast cell activation. There are no effective therapies for CFS. Tricyclic antidepressants have been reported to be beneficial, and our preliminary results indicate that only the tricyclic amitriptyline, and certain natural flavonoids can inhibit mast cell secretion and reduce intracellular calcium ion levels. Our hypothesis is that external triggers, along with CRH secreted by stress, activate diencephalic centers and mast cells, leading to release of proinflammatory and fatigue producing molecules, and these can be inhibited by select flavonoids. We will investigate: (1) the effect of CRH, viral poly(l:C), lipopolysaccharide (LPS), neurotensin (NT), substance P (SP) and thymus stromal lymphopoietin (TSMP) or restraint stress using female C57BL/6 mice on: (a) Fatigue using the forced water immersion test, (b) BBB disruption by measuring brain levels of the fluorescent marker AngioSense, as well as (c) Brain expression of histidine decarboxylase (HDC), CRN, beta-endorphin, IL-6, IL- 8, IL-17, somatostatin, TNF, mouse mast cell protease (MMCP), urocortin 2, UCP2 and VEGF; (2) The requirement for mast cells, for NT, SP, the CRHR involved, and the role of UCP2 in the endpoints studied in Aim 1 by using C57BL-derived WW mast cell deficient mice, NT -/- mice, SP -/- mice, CRHR-1; CRHR-2 -/- and UCP2 -/- mice, (3) Inhibitory effect of a flavonoid formulation containing luteolin/quercetin/olive kernel oil on endurance and brain biomarkers. The proposed research is hypothesis-driven, is based on strong preliminary evidence, is innovative with high likelihood for novel findings with applicability to humans.